Our long term view is toward establishing the qualitative and quantitative characteristics of the function of the surface gastric epithelium in transforming the secretions proffered to it before their transfer to the duodenum so that we may: a) further elucidate the mechanisms whereby the primary highly acid secretion of the gastric glands (160 mEq/L) is modified, and test two current hypotheses (the 2 component and the back-diffusion/exchange hypotheses) which we believe do not account completely for our preliminary observed data; b) elucidate the role of the "more permeable" antrum in intragastric neutralization in the intact stomach as well as the relationship of these characteristics to inhibition and stimulation of gastrin secretion and to the relatively high incidence of acid peptic ulceration in the antrum; c) answer the question as to whether a primary disturbance in the "barrier function" of the surface gastric mucosal membrane exists in patients with primary peptic ulcer and stress or adrenal-steroid gastric ulcer; d) determine if increased loss of secreted acid from the gastric lumen and concomitant alterations in the movement of water and electrolytes, may account for some or all of the aberrations of recovered gastric "secretions" found in certain disorders such as gastric ulcer and the gastric atrophy of pernicious anemia; e) explore some possibly protective or destructive factors of extragastric origin such as saliva, bile, adrenal steroids and drugs as well as some of the functioning of the surface gastric mucosa; f) determine if duodenal ulcer patients have decreased gastric permeability which results in part in the high acid values during secretory tests as well as in the location of the ulcer.